Beefy Boxes and Bandwidth Generously Provided by pair Networks
Clear questions and runnable code
get the best and fastest answer
 
PerlMonks  

Re^2: Is map's sub block really being evaluated in list context? wantarray() returns undef..

by moritz (Cardinal)
on Oct 20, 2011 at 10:35 UTC ( #932615=note: print w/ replies, xml ) Need Help??


in reply to Re: Is map's sub block really being evaluated in list context? wantarray() returns undef..
in thread Is map's sub block really being evaluated in list context? wantarray() returns undef..

Curiously, if you define your own sub which takes a block, wantarray treats it as a normal routine:

$ perl -wE 'sub f(&) { shift->() }; say f { wantarray }' 1

I wonder if this inconsistency is worth a bug report.


Comment on Re^2: Is map's sub block really being evaluated in list context? wantarray() returns undef..
Download Code
Re^3: Is map's sub block really being evaluated in list context? wantarray() returns undef..
by BrowserUk (Pope) on Oct 20, 2011 at 15:07 UTC

    I suspect that as a built-in, map avails itself of more optimisations than it would be safe to apply to a user-written function.

    I know from experience that if you implement a callback interface in XS using the full belts'n'braces approach described in perlcall, then the result is far less efficient than the carefully optimised callback interface used by List::Util::reduce().

    The downside of trying to match that level of optimisation with your own XS code is that it is very easy to create the situation whereby the callback leaks memory if it contains closures. (The early versions of reduce() suffered from the same problems.)

    I think it would be very difficult, if not impossible to compile user-written, runtime-compiled subs taking callbacks, to be as efficient as map. And to 'fix the inconsistency' would essentially require pessimising the implementation of map

    So no, I don't think it is worth a bug report. At most, a documentation change noting the difference might be useful.


    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://932615]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others examining the Monastery: (10)
As of 2014-08-01 10:21 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    Who would be the most fun to work for?















    Results (1 votes), past polls